A time division multiple access (TDMA) multiplexer for video signals has as its inputs a plurality of video channels and is controlled to output only one channel at a time at an output port. One use of such a video multiplexer which will become increasingly more popular is in the area of video on-demand. The video provider supplies a different video program on each channel, encodes each video program in accordance with an accepted compression standard (e.g., an MPEG standard), and then multiplexes all the video channels on a single network cable, which may be an electrical conductor or a fiber optic cable. In video on-demand, one of the plurality of video programs multiplexed on the communications network is selected by the customer, and this video selection is then demultipelxed and displayed on the customer's television set.
Other uses of video multiplexers exist. Existing video multiplexers have various drawbacks. One drawback is that these video multiplexers are relatively expensive, for example over five thousand dollars for a particular four-port multiplexer.
In one prior art multiplexer, each video channel provides raw MPEG encoded video signals to the input of the multiplexer. The multiplexer polls each channel in sequence to determine whether the channel is ready to transmit its video data over the network. When a channel is granted access to the network, the multiplexer then synchronizes and packetizes the video signals for that channel in accordance with a certain protocol and applies the packet to a network interface. The network interface modulates the data in the packet and places the packet in the proper form for being transmitted on the network. Such a prior art multiplexer is sometimes referred to as an asynchronous transfer mode (ATM) switch. Such an ATM switch has a fixed number of ports, is difficult to expand for additional ports, is expensive, and a single ATM switch is not compatible with a variety of types of networks due to the bandwidth limitations of either the ATM switch or the network.
An additional drawback of the prior art video multiplexers is that the bandwidth allocated for each channel is either fixed or not dynamically controllable to allow adjustment for high bandwidth channels. Further, the polling of each channel adds overhead to the system which delays its responsiveness to the changing needs of the various channels.
What is needed is a more economical multiplexer that is flexible enough to be used with virtually any network and is responsive to the changing needs of the various channels.